常压塔顶循环管道腐蚀泄漏原因分析

Analysis on Causes of Corrosion Leakage of Atmospheric Tower Overhead Recycle Line

某石化厂常顶循管道在开工三个月后相继出现腐蚀开裂泄漏现象。通过合金元素分析、铁素体含量测定、内窥镜检查等，并结合实际运行的工况环境对顶循管道腐蚀开裂原因进行了综合分析。结果表明：常顶循管妙管件材质均为双相不锈钢2205，各焊条材质均为双相不锈钢2507；常压塔顶循环管道不同泄漏部位均处于焊道及焊道热影响区，并且铁素体含量较双相钢的正常含量（相比例为35％～65％）相比存在明显偏低现象；结合氯离子含量过高的使用环境，确定氯化物应力腐蚀开裂是造成双相不锈钢管道开裂破坏的主要原因；从设备材质控制和工艺防腐两方面提出了防腐建议和措施。

The corrosion cracking and leakage appeared in the atmospheric tower overhead recycle line 3 months after start - up in a refinery. The root causes of corrosion cracking and leakage are studied through the analysis of alloy element, determination of ferrite content and testing of endoscopy and in consideration of actual operation. The results show that, the material of pipe/pipe fittings of atmospheric tower overhead is duplex stainless steel 2205 and the welding rod is duplex steel 2507 ; The leakages are located in the welding seam and welding bead＇ s heat affected zone; The ferrite content is significantly lower than the normal content （35 % -65 % ） of duplex stainless steel; In consideration of condition of high concentration chloride ions, it is deduced that chloride stress corrosion cracking is the major cause of the duplex stainless steel pipeline cracking and destruction; Corresponding protection measures are proposed from two aspects of equipment material control and process corrosion prevention in view of the leakage causes.